1、Java運算符優先級：
Operator Precedence
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Operators
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Associativity
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[] . () (method call)
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Left to right
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! ~ ++ -- + (unary) – (unary) ()
(cast) new
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Right to left
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* / %
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Left to right
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+ -
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Left to right
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<< >> >>>
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Left to right
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< <= > >= instanceof
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Left to right
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== !=
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Left to right
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&
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Left to right
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^
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Left to right
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Left to right
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&&
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Left to right
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||
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Left to right
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?:
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Right to left
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= += -= *= /= %= &= |= ^= <<= >>=
>>>=
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Right to left
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注意：
- && || ! 的操作數只能用于boolean 或 Boolean
- &? | 的操作數既可以用于boolean(Boolean)或者整形(不僅僅是int型），但兩個操作數的類型必須一致
- ~不能用于boolean(Boolean)型，但可以用于整形，大概是為了和 ! 區別開來吧
- & | 沒有短路計算的
2、
Java Integer Types
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Type
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Storage Requirement
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Range
(Inclusive)
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int
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4 bytes
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–2,147,483,648 to 2,147,483,647 (just over 2 billion)
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short
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2 bytes
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–32,768 to 32,767
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long
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8 bytes
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–9,223,372,036,854,775,808 to
9,223,372,036,854,775,807
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byte
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1 byte
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–128 to 127
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?????
char?? ?? ?? ?? ????????? ? 2 bytes? ?? ?? ?? ?? ?? ?? ?? ????? 0 to 65535
3、
Floating-Point Types
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Type
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Storage Requirement
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Range
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float
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4 bytes
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approximately ±3.40282347E+38F (6–7 significant decimal
digits)
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double
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8 bytes
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approximately ±1.79769313486231570E+308 (15 significant decimal
digits)
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4、final 實例域（final instance field)：可以將實例域定義為final，構建對象時必須初始化這樣得域，也就是說，必須確保在每一個構造器執行之后，這個域的值被設置。但是，靜態常量必須在聲明的同時也被初始化。
5、for each 循環：
for (variable : collection) statment
例如：for (int element : a)
??? ?? ?? System.out.println(element);
該代碼片段打印數組a的每一個元素，一個元素占一行
6、合法的Java標識符：可以以下劃線、字母或美元符號$開頭，后面可以跟下劃線、數字、字母、美元符號。1.42以后的java標識符也可以包含漢字，包括開頭。